X-Git-Url: https://git.distorted.org.uk/~mdw/sod/blobdiff_plain/e0808c472145fc81e52898bc9ac289e10c4f4f41..fddbedf7b1b4b19add30eeb62281748cc77e6955:/src/parser/parser-proto.lisp

diff --git a/src/parser/parser-proto.lisp b/src/parser/parser-proto.lisp
index b97cd4b..f7b5993 100644
--- a/src/parser/parser-proto.lisp
+++ b/src/parser/parser-proto.lisp
@@ -87,6 +87,21 @@
 	  failures
 	  :initial-value nil))
 
+(export 'parse-empty)
+(defun parse-empty (&optional value)
+  "Return a parser which parses nothing, successfully.
+
+   The parser returns VALUE and consumes nothing."
+  (lambda () (values value t nil)))
+
+(export 'parse-fail)
+(defun parse-fail (indicator &optional consumedp)
+  "Return a parser which fails.
+
+   The parser reports the INDICATOR and (falsely) claims to have consumed
+   input if CONSUMEDP is true."
+  (lambda () (values indicator nil consumedp)))
+
 ;;;--------------------------------------------------------------------------
 ;;; Basic protocol.
 
@@ -591,7 +606,7 @@
    The return value may later be used with `parser-restore-place'.  Be
    careful: all of this is happening at macro-expansion time.")
     (:method (context)
-      (error "Parser context ~S doesn't support rewinding." context)))
+      (error "Parser context ~S doesn't support rewinding" context)))
 
   (export 'parser-restore-place)
   (defgeneric parser-restore-place (context place)
@@ -646,7 +661,8 @@
 	   `(let ((,,place ,(parser-capture-place ,context)))
 	      ,(if (parser-places-must-be-released-p ,context)
 		   `(unwind-protect ,(,bodyfunc)
-			,(parser-release-place ,context ,place))
+		      (when ,,place
+			,(parser-release-place ,context ,place)))
 		   (,bodyfunc))))))))
 
 (export 'peek)
@@ -654,12 +670,30 @@
   "Attempt to run PARSER, but rewind the underlying source if it fails."
   (with-gensyms (value win consumedp)
     (with-parser-place (place context)
-      `(multiple-value-bind (,value ,win ,consumedp) (parse ,parser)
-	 (cond (,win
-		(values ,value ,win ,consumedp))
-	       (t
-		,(parser-restore-place context place)
-		(values ,value ,win nil)))))))
+      `(macrolet ((commit-peeked-place ()
+		    `(progn
+		       ,',(parser-release-place context place)
+		       (setf ,',place nil))))
+	 (multiple-value-bind (,value ,win ,consumedp) (parse ,parser)
+	   (cond ((or ,win (null ,place))
+		  (values ,value ,win ,consumedp))
+		 (t
+		  ,(parser-restore-place context place)
+		  (values ,value ,win nil))))))))
+
+(defun commit-peeked-place ()
+  "Called by `commit' not lexically within `peek'."
+  (error "`commit' is not within `peek'"))
+
+(export 'commit)
+(defparse commit ()
+  "Commit to the current parse.
+
+   This releases the place captured by the innermost lexically enclosing
+  `peek'."
+  '(progn
+     (commit-peeked-place)
+     (values nil t nil)))
 
 ;;;--------------------------------------------------------------------------
 ;;; Character parser context protocol.
@@ -845,9 +879,10 @@
    "Return the parser's current token's semantic value."))
 
 (export 'token)
-(defparse token (:context (context token-parser-context)
-		 type &optional (value nil valuep) &key peekp)
-  "Match tokens of a particular type.
+(locally  (declare #+sbcl (sb-ext:muffle-conditions style-warning))
+  (defparse token (:context (context token-parser-context)
+			    type &optional (value nil valuep) &key peekp)
+    "Match tokens of a particular type.
 
    A token matches under the following conditions:
 
@@ -869,35 +904,35 @@
    If the match fails then the failure indicator is either TYPE or (TYPE
    VALUE), depending on whether a VALUE was specified."
 
-  (once-only (type value peekp)
-    (with-gensyms (tokty tokval)
-      `(let ((,tokty ,(parser-token-type context))
-	     (,tokval ,(parser-token-value context)))
-	 (if ,(if (eq type t)
-		  `(not (eq ,tokty :eof))
-		  (flet ((check-value (cond)
-			   (if valuep
-			       `(and ,cond (equal ,tokval ,value))
-			       cond)))
-		    (if (constantp type)
-			(check-value `(eql ,tokty ,type))
-			`(if (eq ,type t)
-			     (not (eq ,tokty :eof))
-			     ,(check-value `(eql ,tokty ,type))))))
-	     ,(let* ((result `(values ,tokval t ,(if (constantp peekp)
-						     (not peekp)
-						     `(not ,peekp))))
-		     (step (parser-step context)))
-		    (cond ((not (constantp peekp))
-			   `(multiple-value-prog1 ,result
-			      (unless ,peekp ,step)))
-			  (peekp
-			   result)
-			  (t
-			   `(multiple-value-prog1 ,result
-			      ,step))))
-	     (values (list ,(if valuep `(list ,type ,value) type))
-		     nil nil))))))
+    (once-only (type value peekp)
+      (with-gensyms (tokty tokval)
+	`(let ((,tokty ,(parser-token-type context))
+	       (,tokval ,(parser-token-value context)))
+	   (if ,(if (eq type t)
+		    `(not (eq ,tokty :eof))
+		    (flet ((check-value (cond)
+			     (if valuep
+				 `(and ,cond (equal ,tokval ,value))
+				 cond)))
+		      (if (constantp type)
+			  (check-value `(eql ,tokty ,type))
+			  `(if (eq ,type t)
+			       (not (eq ,tokty :eof))
+			       ,(check-value `(eql ,tokty ,type))))))
+	       ,(let* ((result `(values ,tokval t ,(if (constantp peekp)
+						       (not peekp)
+						       `(not ,peekp))))
+		       (step (parser-step context)))
+		  (cond ((not (constantp peekp))
+			 `(multiple-value-prog1 ,result
+			    (unless ,peekp ,step)))
+			(peekp
+			 result)
+			(t
+			 `(multiple-value-prog1 ,result
+			    ,step))))
+	       (values (list ,(if valuep `(list ,type ,value) type))
+		       nil nil)))))))
 
 (defmethod expand-parser-spec ((context token-parser-context) spec)
   (if (atom spec)